1. Field of the Invention
The present invention relates generally to a marine propulsion system and, more particularly, to a stern drive unit that provides the capability of adjusting the propeller position vertically without the necessity of providing a U-joint to permit this capability.
2. Description of the Prior Art
Those skilled in the art of marine propulsion systems are aware that most stern drive systems require the use of a U-joint to allow the marine propulsion system to be trimmed, tilted, and steered. Those skilled in the art are also aware that most known stern drive systems do not allow the propeller to be raised or lowered from its normal position without also trimming the drive unit. In addition, those skilled in the art are aware that the steering axis of most known stern drive systems is closer to the transom of a marine vessel than to the intersection between the propeller shaft and the drive shaft which is connected to the propeller shaft.
U.S. Pat. No. 5,647,780, which issued to Hosoi on Jul. 15, 1997, describes a vertically adjustable stern drive for a water craft. The marine stern drive includes a tilt/trim and lift adjustment mechanism which raises and lowers the drive while maintaining an established trim angle. The adjustment mechanism includes a parallelogram linkage system. An upper lever of the linkage system is defined in part by a pair of tilt and trim actuators which vary the length of the upper linkage to adjust the trim position of the stern drive and for tilt up. A lower lever of the linkage system is defined between two flexible couplings of a propulsion drive train. One of the flexible couplings is coupled to a lower drive unit of the stern drive which permits the lower lever to rotate without changing the trim angle of the lower drive unit.
U.S. Pat. No. 4,297,097, which issued to Kiekhaefer on Oct. 27, 1981, discloses a stern drive mechanism. The stern drive installation includes a mounting bracket assembly for securing to the transom of a watercraft. The bracket assembly is provided with a transverse horizontal bore rearwardly of the transom for receiving one end of the horizontal cylinder portion of the upper housing of the drive unit. A bracket assembly addition is provided with a horizontal bore which rotatably receives the opposite end of the horizontal cylindrical portion of the upper housing and is secured to the bracket assembly. The bracket assembly and the addition thereto serve to rotatably support the drive unit and provide for tilt movement of the unit on a horizontal transverse axis. The lower housing of the drive unit is dirigibly connected to the upper housing for support and to provide for pivotal movement of the lower housing relative to the upper housing to provide for steering control of the water craft.
U.S. Pat. No. 6,019,649, which issued to Friesen et al. on Feb. 1, 2000, describes an adjustable propeller system. The system includes an outboard drive portion having a propeller. At least one linearly extendable and retractable trim arm is mounted between an outboard plate and the propeller to adjust the trim angle between the outboard plate and the propeller. An upper arm and a lower arm are each pivotally mounted to a transom mounting plate and typically mounted to the outboard mounting plate. The upper and lower arm are linearly extendable and retractable to adjust the depth of the outboard drive portion.
U.S. Pat. No. 6,383,043, which issued to Heston on May 7, 2002, describes a vertical trim system for marine outdrives. A vertical trim system for a marine inboard-outboard outdrive includes a transom plate and arms having first ends attached to the transom plate and second hands attached to a gimbal ring of the outdrive.
U.S. Pat. No. 5,934,955, which issued to Heston on Aug. 10, 1999, describes a vertical trim system for marine outdrives. The system, for a marine inboard-outboard outdrive, includes a transom plate defining an opening therethrough and having first and second sides, the first side adapted to be mounted to a boat transom. At least one arm includes first and second ends, the first end being pivotally coupled to the second side of the transom plate, such that the arm pivots about a horizontal axis. The second end of the arm is adapted to be pivotally coupled to a gimbal ring of an outdrive.
International Patent Application WO 94/00340, which was filed on Jun. 22, 1993, describes a boat propulsion unit comprising a suspension arrangement and a propeller drive shaft housing which, via a lower and an upper universal joint, are pivotally connected to each other. The suspension arrangement comprises a hollow frame member in the form of an extruded aluminum profile which is fixed around an opening in a boat transom, and a carrier attached to the frame member, said carrier covering the opening and supporting said pivot means. The frame member presents inlets and outlets for exhaust gases.
International Patent Application WO 99/22989, which was filed on Nov. 3, 1998, describes an omni-directional horizontal thrust adjustable marine propulsion system. The system is capable of providing independent control of propeller elevation, trim and steering utilizes a set of pivotally connected, independent frames. A pair of elevational hydraulic rams are connected between the vessel and the frame support for controlling the lift of the propeller. A trim hydraulic ram, coupled between the support frame and the upper gearcase controls the trim. Directional control is provided by a drive shaft coupled between the gear cases.
International Patent Application WO 91/19644, which was filed on Jun. 20, 1991, describes an arrangement in connection with a swingable turn-up inboard/outboard stern aggregate for a craft. An arrangement in a swingable turn-up inboard/outboard stern aggregate for a craft with an inboard engine and an outboard driving means comprises a screw, where the inboard driving shaft of the stern aggregate for connection with the engine is connected with a screw shaft which is approximately horizontal in a position for use and is mounted in the lower end of a housing by the aid of a transmission shaft, which is divided into two sections and surrounded by a housing. The first section is at one end mounted in the upper end of the housing and connected with the driving shaft, via a first universal joint, and is at its other end, via an angular gear, connected with an upper end of a section which is inclined rearwards and downwards. The lower end of the second section is connected with a screw shaft at a firm angle, via a transmission means of torsional moment. In connection with the angular gear comprising two sets of angular gear wheels, a reversing means is provided to reverse the direction of rotation of the lower section and, thus, the direction of movement of the craft.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In certain types of marine propulsion systems, the U-joint is susceptible to wear and damage. Most known stern drive systems require the use of at least one U-joint in order to allow the system to move for the purpose of trimming or steering the drive unit relative to the transom of a boat. In addition, most known stern drive systems do not allow for the raising or lowering of a propeller shaft without a corresponding change in the trim of the drive. Typically, changing the elevation of the propeller shaft relative to the boat requires significant changes to the overall marine propulsion system.
It would therefore be significantly beneficial if a marine propulsion system could be provided which allows a stern drive unit to be raised or lowered without requiring a change in the trim angle of the drive unit. It would also be significantly beneficial if the stern drive unit could be provided which allows the propeller shaft to be steered about a steering axis which is coincident with the generally vertical drive shaft axis of rotation.